NM vs. CM

If you look at chess.com titled players, there are GM's, IM's, FM's, CM's, and NM's. I know Grandmaster is highest, of course, followed by International Master, then followed by FIDE Master. Candidates Master and National Master don't require a norm, just a rating of 2200+. If there is no difference between the 2 (and if there is a difference please tell me) why do some choose to be listed as an NM, and some as a CM?

NM is an American title. It is part of a different hierarchy than CM.

FM requires no norms either 

The difference between CM and NM is that CM is a FIDE title for 2200 FIDE rating and NM is not . NM is a national rating (uscf) of 2200 or better. Other countries ( like Portugal ) also give the NM title for 2200 FIDE rating.......